Seattle defeated Kelowna on Saturday 2-1 in overtime to take a 2-0 series lead, despite being the heavy underdog.
The Thunderbirds, who entered the playoffs as the seventh seed in the Western Conference, finished the regular season with 28 fewer wins and 50 less points than the second-seeded Rockets. Kelowna also had a league-best record on home ice of 31-5-0, while Seattle's .333 win percentage on the road was third last in the WHL.
Rookie Alexander Delnov scored his first-career playoff goal 2:41 into extra time to give Seattle their second victory of the series by way of sudden death.
The Thunderbirds were victorious in Game 1 on Friday after downing the Rockets 5-4 on a Luke Lockhart overtime goal.
Third-year defenceman Jared Hauf also recorded his first post-season goal for the Thunderbirds while Brandon Glover stopped 21 shots for the victory
Cole Linaker responded for the Rockets, who dropped back-to-back home games only once all season.
Jordon Cooke made 17 saves in defeat and has now allowed seven goals on 69 shots in the series.
Both clubs went 0 for 3 on the power play.
Game 3 is set for Tuesday when Seattle hosts Kelowna at the ShoWare Center.